The follicle stimulating hormone receptor (FSHR) and FSH play crucial roles in reproduction of mammal. Mutant FSHR and FSH are involved in fertility disorders, while FSHR and FSH are thought to be associated with ovarian and prostate cancers. Our long term goal is to understand the molecular mechanisms of FSHR's activities, which necessitates the study of interaction between FSHR and FSH and subsequent generation of signals for second messengers, cAMP and inositol phosphates. FSHR and other glycoprotein hormone receptors belong to a structurally unique subfamily of G protein-coupled receptors. They consist of the extracellular N-terminal half with approximately 350 amino acids (exodomain) and the membrane associated C-terminal half with an equal number of amino acids (endodomain). Since we and others reported, nearly ten years ago, that the exodomain is capable of high affinity hormone binding and signal generation, that the exodomain is the only high affinity binding site, and that the hormone/exodomain complex undergoes a conformation adjustment. Based on these observations we proposed that the hormone/exodomain complex interacts with the endodomain and this secondary interaction is responsible for signal generation. Lately, many of these have been verified and adopted by others. During the past grant period, we have reported a number of novel observations that hormone binding and signal generation of FSHR are distinct events, that exoloops in the endodomain constrain the FISH binding to the exodomain, and that FSH binding and cAMP induction work against each other and are compromised to maintain both activities at reasonable levels. Our preliminary findings suggest that the signals for cAMP and inositol phosphates are distinct, that the signals for inositol monophosphate, inositol biophosphate, and inositol triphosphate are also distinct, and that the putative Leu Rich Repeat motif in the exodomain is in need involved in FSH binding. Finally, we have found that the exodomain of one FSHR intermolecularly interacts with the endodomain of another FSHR, which has a significant implication in the understanding for the mechanism of multiple signal generation by not only FSHR but also other G protein coupled receptors. We propose to extend our observations (1) to determine the roles of individual amino acids in exoloops on hormone binding and induction of cAMP and three IP species, (2) to identify the contact points among the hormone, exodomain and endodomain, and (3) to conclusively demonstrate the intermolecular interaction of exodomain and endodomain and to examine the mechanisms. When successfully carried out, these studies will have far reaching consequences in understanding the underlying mechanisms of multiple signal generations by a FSHR as well as other receptors have significant implications in clinical and industrial applications.